CVE-2026-7721 Overview
CVE-2026-7721 is a command injection vulnerability affecting the Totolink WA300 router running firmware version 5.2cu.7112_B20190227. The flaw resides in the NTPSyncWithHost function within /cgi-bin/cstecgi.cgi. Attackers can manipulate the hostTime argument to inject operating system commands. The issue is classified under CWE-74 for improper neutralization of special elements in output used by a downstream component. The vulnerability is remotely reachable over the network and requires only low-level privileges. Public disclosure of the exploit details has occurred via VulDB and a third-party Notion writeup.
Critical Impact
Authenticated remote attackers can inject arbitrary shell commands into the hostTime parameter, gaining command execution on affected Totolink WA300 devices.
Affected Products
- Totolink WA300 router
- Firmware version 5.2cu.7112_B20190227
- Web management endpoint /cgi-bin/cstecgi.cgi
Discovery Timeline
- 2026-05-04 - CVE-2026-7721 published to NVD
- 2026-05-04 - Last updated in NVD database
Technical Details for CVE-2026-7721
Vulnerability Analysis
The vulnerability exists in the NTPSyncWithHost handler within the CGI binary /cgi-bin/cstecgi.cgi on the Totolink WA300. This handler accepts a hostTime parameter intended to specify an NTP host for time synchronization. The handler passes the parameter into a shell command without sanitizing shell metacharacters. An attacker who can reach the device's HTTP management interface can submit a crafted request that breaks out of the intended command structure. The injected payload executes with the privileges of the CGI process, which on consumer routers typically equates to root. The EPSS probability is 3.681% with a percentile of 87.986, indicating elevated relative likelihood of exploitation activity compared to the broader CVE population.
Root Cause
The root cause is improper neutralization of special elements passed to a downstream OS shell, mapped to [CWE-74]. The NTPSyncWithHost function concatenates user-supplied input from hostTime directly into a system command invocation without validation, escaping, or use of safe execution APIs. Shell metacharacters such as ;, |, and backticks are interpreted by the shell rather than treated as literal data.
Attack Vector
The attack is performed remotely over the network against the device's HTTP interface. An attacker sends a POST request to /cgi-bin/cstecgi.cgi with a JSON body invoking the NTPSyncWithHost action and a malicious hostTime value containing shell metacharacters. Exploitation requires low-level privileges on the device, consistent with the published CVSS metrics. Public proof-of-concept material referenced through VulDB Vulnerability #360897 and the Notion Document Analysis describes the exploitation path. No verified exploit code is reproduced here; refer to the linked references for technical details.
Detection Methods for CVE-2026-7721
Indicators of Compromise
- HTTP POST requests to /cgi-bin/cstecgi.cgi containing the NTPSyncWithHost action with shell metacharacters such as ;, &&, |, or backticks in the hostTime field.
- Unexpected outbound connections from the router to attacker-controlled infrastructure shortly after CGI requests.
- New or modified processes spawned from cstecgi.cgi that are not part of normal NTP synchronization activity.
Detection Strategies
- Inspect inbound HTTP traffic to the router management interface for NTPSyncWithHost payloads with non-hostname characters in hostTime.
- Apply IDS/IPS signatures matching command injection patterns against /cgi-bin/cstecgi.cgi request bodies.
- Correlate router syslog entries with subsequent network anomalies originating from the device.
Monitoring Recommendations
- Forward router logs to a centralized logging or SIEM platform for retention and correlation.
- Monitor for management interface exposure to untrusted networks, including WAN-side accessibility.
- Track firmware version inventory to identify devices still running 5.2cu.7112_B20190227.
How to Mitigate CVE-2026-7721
Immediate Actions Required
- Restrict access to the router's HTTP management interface to trusted internal networks only and disable WAN-side administration.
- Change default and weak administrative credentials, since exploitation requires authenticated access at low privilege.
- Audit the device for signs of prior exploitation, including unexpected configuration changes or new services.
Patch Information
No vendor patch is referenced in the available CVE data at the time of publication. Consult the TOTOLINK Official Website for firmware updates and security advisories. Affected operators should track vendor releases for firmware addressing the NTPSyncWithHost input handling.
Workarounds
- Place the WA300 behind a network segment that blocks untrusted clients from reaching /cgi-bin/cstecgi.cgi.
- Disable remote management features and any NTP configuration UI exposure where operationally feasible.
- Replace end-of-support hardware with currently supported models if no firmware fix becomes available.
# Configuration example: block external access to the router admin interface
# Example iptables rule applied on an upstream gateway
iptables -A FORWARD -d <router-ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router-ip> -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
